CN113325333A - Small current grounding system disconnection detection method suitable for fault indicator - Google Patents
Small current grounding system disconnection detection method suitable for fault indicator Download PDFInfo
- Publication number
- CN113325333A CN113325333A CN202110526368.1A CN202110526368A CN113325333A CN 113325333 A CN113325333 A CN 113325333A CN 202110526368 A CN202110526368 A CN 202110526368A CN 113325333 A CN113325333 A CN 113325333A
- Authority
- CN
- China
- Prior art keywords
- fault
- phase
- disconnection
- value
- current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/54—Testing for continuity
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
Abstract
The invention discloses a small current grounding system disconnection detection method suitable for a fault indicator, which comprises the following steps: step 1, determining fault time by monitoring three-phase voltage change; step 2, calculating the phase relation of the voltage before and after the fault, and determining the three-phase sequence before and after the fault; step 3, calculating effective values of the current before and after the fault; and 4, comparing the three-phase sequence before and after the fault with the change of the three-phase current effective value, and judging whether the upstream of the detection point has the disconnection fault. Compared with the traditional power distribution terminal for judging the disconnection fault, the fault indicator is cheaper and has stronger applicability, and the method realizes the disconnection fault judgment by using the fault indicator without depending on line voltage and phase voltage amplitude data.
Description
Technical Field
The invention relates to the technical field of distribution network automation, in particular to a small current grounding system disconnection detection method suitable for a fault indicator.
Background
In a small current grounding system, namely a system with a neutral point not grounded and a system with a neutral point grounded through an arc suppression coil, after a disconnection fault occurs, the voltage changes obviously.
In the past, the detection and judgment of the disconnection fault mainly depend on the change of line voltage, and a fault indicator is limited by a voltage acquisition method, so that the line voltage cannot be measured, and the amplitude of phase voltage is not accurately measured, so that the occurrence of the disconnection fault cannot be judged. Therefore, it is desirable to find a method of line break fault detection that does not rely on line voltage and phase voltage magnitude.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention provides the small current grounding system disconnection detection method suitable for the fault indicator, which does not need to rely on line voltage and phase voltage amplitude data and realizes the judgment of disconnection faults by utilizing the fault indicator.
The purpose of the invention can be realized by the following technical scheme:
a small current grounding system disconnection detection method suitable for a fault indicator comprises the following steps:
step 1: determining the fault moment by monitoring the change of the effective value of the three-phase voltage, the change of the instantaneous value of the three-phase voltage or the change of the amplitude value of the three-phase voltage;
step 2: randomly selecting data of 1 power frequency period length or multiple length thereof before the fault, recording the data as voltage before the fault, randomly selecting data of 1 power frequency period length or multiple length thereof after the fault, recording the data as voltage after the fault, calculating a phase relation by comparing zero crossing point time or an FFT algorithm, and determining a three-phase sequence before the fault and after the fault;
and step 3: randomly selecting data of 0.5 power frequency period length or multiple length thereof before the fault, recording the data as current before the fault, randomly selecting data of 0.5 power frequency period length or multiple length thereof after the fault, recording the data as current after the fault, and calculating effective values of current before and after the fault;
and 4, step 4: and comparing the three-phase sequence before and after the fault with the change of the three-phase current effective value, and judging whether the upstream of the detection point has the disconnection fault or not.
Further, the method for monitoring the change of the effective value of the three-phase voltage in the step 1 comprises the following steps:
and calculating an effective value once for each half power frequency of each phase voltage, and recording the initial moment of calculating the effective value once as the fault occurrence moment if the difference value between the two effective values before and after one phase voltage exceeds a threshold value.
Further, the method for monitoring the change of the instantaneous values of the three-phase voltage to determine the fault time in the step 1 comprises the following steps:
and if the instantaneous value of one-phase voltage exceeds the expected threshold value at the corresponding moment, recording the moment as the fault occurrence moment.
Further, the method for monitoring the amplitude change of the three-phase voltage to determine the fault time in the step 1 comprises the following steps:
and searching a maximum value once for each half power frequency of each phase voltage, and if the difference value between the two maximum values before and after one phase voltage exceeds a threshold value, recording the initial moment of calculating the effective value at the last time as the fault occurrence moment.
Further, the method for calculating the phase in step 2 is as follows:
and marking the three-phase voltage as an A phase, a B phase and a C phase respectively, comparing the zero crossing point time or the phase size extracted by FFT, and sequencing to obtain a phase sequence, wherein ABC, BCA and CAB are the same phase sequence, and ACB, CBA and BAC are the same phase sequence.
Further, the comparing and determining method in step 4 is as follows:
and if the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than a set threshold value a and the phase difference of the three-phase voltage after the fault is smaller than a threshold value b, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position.
Further, the comparison and determination method in step 4 may be:
and if the phase sequence before the fault is different from the phase sequence after the fault and the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than the set threshold value a, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position.
Further, the value range of the threshold value a is 0-1.2.
Further, the value range of the threshold b is 0-60 °.
The invention has the beneficial technical effects that: compared with the traditional power distribution terminal for judging the disconnection fault, the fault indicator is cheaper and has stronger applicability, and the method realizes the disconnection fault judgment by using the fault indicator without depending on line voltage and phase voltage amplitude data.
Drawings
FIG. 1 is a general flow diagram of the present invention.
FIG. 2 is a waveform of a measured voltage in an embodiment of the present invention.
FIG. 3 is a waveform of a measured current in an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
As shown in fig. 1, a method for detecting a broken line of a low-current grounding system suitable for a fault indicator, which is used for judging broken line fault recording shown in fig. 2 and 3, includes the following steps:
step 1: determining the fault moment by monitoring the change of the effective value of the three-phase voltage, the change of the instantaneous value of the three-phase voltage or the change of the amplitude value of the three-phase voltage;
the method for monitoring the change of the effective value of the three-phase voltage comprises the following steps: and calculating an effective value once for each half power frequency of each phase voltage, and recording the initial moment of calculating the effective value once as the fault occurrence moment if the difference value between the two effective values before and after one phase voltage exceeds a threshold value.
The method for monitoring the change of the three-phase voltage instantaneous value to determine the fault moment comprises the following steps: and if the instantaneous value of one-phase voltage exceeds the expected threshold value at the corresponding moment, recording the moment as the fault occurrence moment.
The method for monitoring the change of the three-phase voltage amplitude to determine the fault moment comprises the following steps: and searching a maximum value once for each half power frequency of each phase voltage, and if the difference value between the two maximum values before and after one phase voltage exceeds a threshold value, recording the initial moment of calculating the effective value at the last time as the fault occurrence moment.
In the embodiment, a method for monitoring the change of the effective value of the three-phase voltage is adopted, and the fault occurrence time is determined to be 0.13s by the method.
Step 2: randomly selecting data of 1 power frequency period length or multiple length thereof before the fault, recording the data as voltage before the fault, randomly selecting data of 1 power frequency period length or multiple length thereof after the fault, recording the data as voltage after the fault, calculating a phase relation by comparing zero crossing point time or an FFT algorithm, and determining a three-phase sequence before the fault and after the fault; the method for calculating the phase comprises the following steps:
and marking the three-phase voltage as an A phase, a B phase and a C phase respectively, comparing the zero crossing point time or the phase size extracted by FFT, and sequencing to obtain a phase sequence, wherein ABC, BCA and CAB are the same phase sequence, and ACB, CBA and BAC are the same phase sequence.
As shown in fig. 2, in the embodiment, 0.06 s-0.08 s of voltage data before a fault is selected and recorded as voltage before the fault, 0.14 s-0.16 s of voltage data after the fault is selected and recorded as voltage after the fault, and the phase relationship is calculated by comparing the zero crossing points, wherein the phase a before the fault leads the phase B by 120 degrees, the phase B leads the phase C by 120 degrees, and the phase sequence is ABC; after the fault, the phase B leads the phase A by 30 degrees, the phase A leads the phase C by 30 degrees, and the phase sequence is BAC;
and step 3: randomly selecting data of 0.5 power frequency period length or multiple length thereof before the fault, recording the data as current before the fault, randomly selecting data of 0.5 power frequency period length or multiple length thereof after the fault, recording the data as current after the fault, and calculating effective values of current before and after the fault;
in the embodiment, as shown in fig. 3, current data of 0.06s to 0.08s before the fault is selected and recorded as the current before the fault, current data of 0.14s to 0.16s after the fault is selected and recorded as the current after the fault, and the effective values of A, B, C three-phase currents before the fault are calculated to be 5.7A, 5.7A and 5.7A respectively, and the effective values of A, B, C three-phase currents after the fault are 0A, 4.9A and 4.2A respectively.
And 4, step 4: and comparing the three-phase sequence before and after the fault with the change of the three-phase current effective value, and judging whether the upstream of the detection point has the disconnection fault or not. The specific comparison and judgment method comprises the following steps:
and if the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than a set threshold value a and the phase difference of the three-phase voltage after the fault is smaller than a threshold value b, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position. Wherein the value range of the threshold value a is 0-1.2, and the value range of the threshold value b is 0-60 degrees.
The comparison and judgment method can also be as follows:
and if the phase sequence before the fault is different from the phase sequence after the fault and the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than the set threshold value a, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position.
In the embodiment, the phase difference value of the three-phase voltage after the fault is not less than the threshold (in the embodiment, the threshold is set to be 25 °), the phase sequence before the fault is not the same, the current effective value ratios of A, B, C three-phase voltage after the fault and current effective value values before the fault are respectively 0, 8.6 and 0.74, and are all less than the threshold (in the embodiment, the threshold is set to be 1.2), the waveform is considered to be recorded as a broken line fault waveform, and the broken line position is upstream of the detection point of the waveform.
The above-mentioned embodiments are illustrative of the specific embodiments of the present invention, and are not restrictive, and those skilled in the relevant art can make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention, so that all equivalent technical solutions should be included in the scope of the present invention.
Claims (9)
1. A small current grounding system disconnection detection method suitable for a fault indicator is characterized by comprising the following steps:
step 1: determining the fault moment by monitoring the change of the effective value of the three-phase voltage, the change of the instantaneous value of the three-phase voltage or the change of the amplitude value of the three-phase voltage;
step 2: randomly selecting data of 1 power frequency period length or multiple length thereof before the fault, recording the data as voltage before the fault, randomly selecting data of 1 power frequency period length or multiple length thereof after the fault, recording the data as voltage after the fault, calculating a phase relation by comparing zero crossing point time or an FFT algorithm, and determining a three-phase sequence before the fault and after the fault;
and step 3: randomly selecting data of 0.5 power frequency period length or multiple length thereof before the fault, recording the data as current before the fault, randomly selecting data of 0.5 power frequency period length or multiple length thereof after the fault, recording the data as current after the fault, and calculating effective values of current before and after the fault;
and 4, step 4: and comparing the three-phase sequence before and after the fault with the change of the three-phase current effective value, and judging whether the upstream of the detection point has the disconnection fault or not.
2. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator as claimed in claim 1, wherein the method for monitoring the change of the effective value of the three-phase voltage in the step 1 is as follows:
and calculating an effective value once for each half power frequency of each phase voltage, and recording the initial moment of calculating the effective value once as the fault occurrence moment if the difference value between the two effective values before and after one phase voltage exceeds a threshold value.
3. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 1, wherein the method for monitoring the instantaneous change of the three-phase voltage to determine the fault moment in the step 1 comprises the following steps:
and if the instantaneous value of one-phase voltage exceeds the expected threshold value at the corresponding moment, recording the moment as the fault occurrence moment.
4. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 1, wherein the method for monitoring the amplitude change of the three-phase voltage to determine the fault moment in the step 1 comprises the following steps:
and searching a maximum value once for each half power frequency of each phase voltage, and if the difference value between the two maximum values before and after one phase voltage exceeds a threshold value, recording the initial moment of calculating the effective value at the last time as the fault occurrence moment.
5. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator in claim 1, wherein the method for calculating the phase in the step 2 is as follows:
and marking the three-phase voltage as an A phase, a B phase and a C phase respectively, comparing the zero crossing point time or the phase size extracted by FFT, and sequencing to obtain a phase sequence, wherein ABC, BCA and CAB are the same phase sequence, and ACB, CBA and BAC are the same phase sequence.
6. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 1, wherein the comparing and determining method in the step 4 is as follows:
and if the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than a set threshold value a and the phase difference of the three-phase voltage after the fault is smaller than a threshold value b, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position.
7. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 1, wherein the comparing and determining method in the step 4 can also be:
and if the phase sequence before the fault is different from the phase sequence after the fault and the ratio of the effective value of the three-phase current after the fault to the effective value of the three-phase current before the fault is smaller than the set threshold value a, the occurrence of the disconnection fault is determined, and the detection point is positioned at the downstream of the disconnection position.
8. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 6, wherein the value of the threshold value a ranges from 0 to 1.2.
9. The method for detecting the disconnection of the low-current grounding system suitable for the fault indicator according to claim 6, wherein the value of the threshold b ranges from 0 ° to 60 °.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110526368.1A CN113325333A (en) | 2021-05-14 | 2021-05-14 | Small current grounding system disconnection detection method suitable for fault indicator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110526368.1A CN113325333A (en) | 2021-05-14 | 2021-05-14 | Small current grounding system disconnection detection method suitable for fault indicator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN113325333A true CN113325333A (en) | 2021-08-31 |
Family
ID=77415760
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202110526368.1A Pending CN113325333A (en) | 2021-05-14 | 2021-05-14 | Small current grounding system disconnection detection method suitable for fault indicator |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN113325333A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114895149A (en) * | 2022-07-13 | 2022-08-12 | 石家庄科林电气股份有限公司 | Power distribution network disconnection fault detection method and detection terminal |
Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102955098A (en) * | 2012-12-10 | 2013-03-06 | 四川省电力公司资阳公司 | Neutral point non-effective earthing system single-phase earthing fault identification method |
| CN104297629A (en) * | 2014-08-19 | 2015-01-21 | 中国科学院电工研究所 | Method for detecting and positioning section faults of a power distribution network containing distributed generators |
| CN104777397A (en) * | 2015-04-16 | 2015-07-15 | 王金泽 | Distribution line single-phase break line judgment and positioning method based on line voltage vector criterion |
| CN105137365A (en) * | 2015-08-31 | 2015-12-09 | 湖南省普安建设工程有限公司 | Three-phase power monitoring system and method |
| CN106646139A (en) * | 2016-12-30 | 2017-05-10 | 华北电力大学 | Method for positioning faults of power distribution network based on amplitude analysis of three-phase current |
| CN108548990A (en) * | 2018-04-04 | 2018-09-18 | 国电南瑞科技股份有限公司 | Telegram in reply Proposals method based on electric network fault behavioural analysis |
| CN109061384A (en) * | 2018-08-13 | 2018-12-21 | 国网湖南省电力有限公司 | A kind of one-phase earthing failure in electric distribution network phase discrimination method and system |
| CN109324269A (en) * | 2018-12-18 | 2019-02-12 | 国网山东省电力公司电力科学研究院 | Power distribution network single-phase disconnection fault identification method based on distributed measurement |
| CN109782108A (en) * | 2019-01-31 | 2019-05-21 | 中国电力科学研究院有限公司 | A kind of single-phase grounded malfunction in grounded system of low current localization method and device |
| CN110850333A (en) * | 2019-11-20 | 2020-02-28 | 吉林松江河水力发电有限责任公司 | Phase identification method for single-phase earth fault of low-voltage distribution system |
| CN111007355A (en) * | 2019-12-11 | 2020-04-14 | 苏州银蕨电力科技有限公司 | Disconnection fault detection method based on wide-area synchronous intelligent sensor |
-
2021
- 2021-05-14 CN CN202110526368.1A patent/CN113325333A/en active Pending
Patent Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102955098A (en) * | 2012-12-10 | 2013-03-06 | 四川省电力公司资阳公司 | Neutral point non-effective earthing system single-phase earthing fault identification method |
| CN104297629A (en) * | 2014-08-19 | 2015-01-21 | 中国科学院电工研究所 | Method for detecting and positioning section faults of a power distribution network containing distributed generators |
| CN104777397A (en) * | 2015-04-16 | 2015-07-15 | 王金泽 | Distribution line single-phase break line judgment and positioning method based on line voltage vector criterion |
| CN105137365A (en) * | 2015-08-31 | 2015-12-09 | 湖南省普安建设工程有限公司 | Three-phase power monitoring system and method |
| CN106646139A (en) * | 2016-12-30 | 2017-05-10 | 华北电力大学 | Method for positioning faults of power distribution network based on amplitude analysis of three-phase current |
| CN108548990A (en) * | 2018-04-04 | 2018-09-18 | 国电南瑞科技股份有限公司 | Telegram in reply Proposals method based on electric network fault behavioural analysis |
| CN109061384A (en) * | 2018-08-13 | 2018-12-21 | 国网湖南省电力有限公司 | A kind of one-phase earthing failure in electric distribution network phase discrimination method and system |
| CN109324269A (en) * | 2018-12-18 | 2019-02-12 | 国网山东省电力公司电力科学研究院 | Power distribution network single-phase disconnection fault identification method based on distributed measurement |
| CN109782108A (en) * | 2019-01-31 | 2019-05-21 | 中国电力科学研究院有限公司 | A kind of single-phase grounded malfunction in grounded system of low current localization method and device |
| CN110850333A (en) * | 2019-11-20 | 2020-02-28 | 吉林松江河水力发电有限责任公司 | Phase identification method for single-phase earth fault of low-voltage distribution system |
| CN111007355A (en) * | 2019-12-11 | 2020-04-14 | 苏州银蕨电力科技有限公司 | Disconnection fault detection method based on wide-area synchronous intelligent sensor |
Non-Patent Citations (2)
| Title |
|---|
| 吴少鹏: "基于对称分量法的外线单相断线故障分析", 《无线发射与节传技术》 * |
| 张芜: "电力系统非全相运行时相序电流和相序电压的关系", 《继电器》 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114895149A (en) * | 2022-07-13 | 2022-08-12 | 石家庄科林电气股份有限公司 | Power distribution network disconnection fault detection method and detection terminal |
| CN114895149B (en) * | 2022-07-13 | 2022-09-30 | 石家庄科林电气股份有限公司 | Power distribution network disconnection fault detection method and detection terminal |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN109103852B (en) | Single-phase earth fault protection method of small-resistance earth system based on zero-sequence current comparison | |
| Lee et al. | An intelligent and efficient fault location and diagnosis scheme for radial distribution systems | |
| CN108448540B (en) | Zero sequence current comparison-based ground fault protection method for small-resistance grounding system | |
| CN101452038A (en) | Low current neutral grounding electric network single-phase earth fault diagnostic method | |
| CN105974254B (en) | The temporary stable state selection method of comprehensive weight is calculated based on voltage | |
| CN111537837A (en) | Method and system for positioning small current ground fault of power distribution network | |
| CN110045232B (en) | Method for identifying ground fault phase of neutral point non-effective grounding system | |
| CN110579684A (en) | low-current grounding system line selection method based on fusion algorithm | |
| CN113325333A (en) | Small current grounding system disconnection detection method suitable for fault indicator | |
| CN110542823A (en) | Distribution line single-phase earth fault section positioning method | |
| CN112379302B (en) | Small-current ground fault protection method, device and system for integrating time-frequency domain information | |
| CN112379213B (en) | Fault detection method and system | |
| CN116148599B (en) | Kurtosis and skewness coefficient-based high-resistance ground fault diagnosis protection method and device | |
| Eissa | Development and investigation of a new high-speed directional relay using field data | |
| CN112485595A (en) | Power distribution network ground fault line selection protection method and device | |
| CN111537838A (en) | Flexible grounding mode power distribution network grounding fault direction algorithm | |
| CN112578198A (en) | Transient current characteristic-based ship MMC-MVDC rapid fault protection method | |
| CN112067944A (en) | Single-phase grounding fault detection control method for power transmission and distribution line | |
| CN113721114B (en) | High-resistance ground fault line selection method, system and storage medium for resonant ground power distribution network | |
| CN115575769A (en) | Power grid fault detection method and system based on mode domain current distribution characteristics | |
| CN115856496A (en) | Distribution line fault detection and identification method based on two-end information acquisition | |
| CN113567803B (en) | Low-current ground fault positioning method and system based on Tanimoto similarity | |
| CN111913078B (en) | Power transmission line fault identification method based on operation | |
| CN112578228A (en) | Zero-sequence-independent single-phase earth fault discrimination algorithm for power distribution network | |
| CN114414944A (en) | Low-current grounding device based on phase current transient method and detection method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| WD01 | Invention patent application deemed withdrawn after publication |
Application publication date: 20210831 |
|
| WD01 | Invention patent application deemed withdrawn after publication |